<!docytpe html>
<html>
<head>
<meta charset="UTF-8" />
<script>
window.onload=function(){

var c=document.getElementById("myCanvas").getContext("2d");

c.fillStyle = "green";

c.fillRect(0, 0,100,100);

c.fillStyle = "red";
c.globalCompositeOperation = "destination-over";
c.rect(0, 0, 100, 100);
c.clip();
c.fillRect(0, 0, 100, 100);

}
</script>
</head>
<body>
<canvas id="myCanvas" height=50 width=100></canvas>
</body>
</html>